Conventional bottles for feeding infants have for years consisted of solid plastic or glass bottles into which the liquid is placed directly, after which the bottle is topped by an appropriate nipple assembly from which an infant can feed. As known to those of ordinary skill in this art--parents--such conventional bottles naturally fill with air as the infant drinks the liquid. In turn, the feeding infant tends to swallow some of the air, causing indigestion.
As an improvement on this long existing configuration, a newer generation of baby nursing bottles consists of a polymeric cylinder into which a collapsible plastic bag can be positioned. The milk, formula, or other liquid is then added to the bag rather than to the cylinder. When topped with the appropriate nipple assembly, this arrangement desirably provides a system under which the bag gradually collapses as the infant feeds from the liquid therein. Because the bag collapses, there is a lesser tendency for air to enter it as an infant drinks. Ideally, this system helps an infant to swallow less air during feeding than the infant would when feeding from a noncollapsible bottle.
Nevertheless, an air content problem remains with such collapsible bag feeding systems in that during normal filling procedures, the collapsible bag can never be filled completely with liquid, and for several reasons. First, the dexterity required to fill the collapsible bag exactly to the top, but no further is somewhat unrealistic to expect during the normal circumstances surrounding feeding an infant. Perhaps more fundamentally, even if the collapsible bag could be exactly and totally filled with liquid, there is still an air space present that results when the nipple assembly is placed on the collapsible bag and the supporting plastic cylinder. Thus, some air almost always remains in the collapsible bag in spite of its other advantages.
Accordingly, a number of structures have been proposed for addressing this problem. In U.S. Pat. No. 3,648,873 to Grobbel a structure is proposed in which a plunger on a separate stand is used to purge air from such a nursing system.
Hammer, U.S. Pat. No. 3,955,698 show a relatively complex spring and plunger system for expelling air from such a nursing system.
Miller, U.S. Pat. No. 4,176,754 shows a "pneumatic biasing member" which attempts to solve the problem.
McKeown, U.S. Pat. No. 4,796,767 shows a pressure applicator having a generally L-shaped cross section for expelling air from the collapsible bag of such a nursing bottle.
Lebeau, U.S. Pat. No. 4,880,125 discloses a relatively straightforward plunger system, but which is rather extensive in length and which, when the bottle is full, effectively doubles the size of the nurser.
Finally, Askerneese, U.S. Pat. No. 4,979,629 discloses an air expeller system for a nursing bottle which includes a storage system for liners, a nipple, and premeasured portions of infant formula. Askerneese illustrates a measuring cup device which, when inverted within the nurser, can be used to expel air from the collapsible bag. As in the case of the Lebeau device, however, when the bottle is full the presence of the inverted cup essentially doubles the effective length of the bottle.
Therefore, the need exists for a simple, straightforward device for expelling air from such nursing bottles which avoids the complexities apparent in the prior art and instead focuses on the straightforward tasks of expelling air.